A.A. Pisano

Closed form solution for a nonlocal elastic bar in tension

A simple mechanical one-dimensional problem in the context of nonlocal (integral) elasticity is solved analytically. The nonlocal elastic material behaviour is described by the ‘‘Eringen model’’ whose nonlocality features all reside in the constitutive relation. This relation, of integral type, contains an attenuation function (usually assumed symmetric) aimed to capture the diffusion process of the nonlocality effects; it also exhibits a convolution format. The governing equation is a Fredholm integral equation of second kind whose analytical treatment, even for the usual choice of a symmetric kernel, is not easy to develop. In the present paper, assuming a specific shape for the attenuation function, a closed form solution in terms of strains is alternatively obtained by solving a Volterra integral equation of second kind. The latter can be easily solved with standard techniques, at least for the adopted kernel, taking also advantage from the symmetry of the solution. Such a closed form solution is an essential result to validate the effectiveness of numerical procedures aimed to solve more complex mechanical problems in the context of nonlocal elasticity. 2002 Elsevier Science Ltd. All rights reserved.

Frequency domain analysis of dynamic response of drag dominated offshore structures

The paper describes a method for stochastic representation of the hydrodynamic drag forces on offshore structures subjected to irregular waves. It is shown that, for the case of zero current, it is possible to construct a genuinely quadratic representation of the drag force which reproduces the statistical properties of the standard formulation of the drag force very closely, and which at the same time has sufficient flexibility to ensure a spectral density that accurately approximates the desired force spectrum. The distinct advantage of the new representation is that it brings dynamic analysis of extensive linear structures back into the frequency domain.

A neural network approach to structure damage assessment

Presents a method for damage detection in multi-bay planar truss structures. A neural network is trained by transfer functions of the structural system. The approach allows one to avoid all the problems which characterize the techniques based on system parameter identification. The neural network architecture and size, the choice of the learning rule and of the corresponding parameters are discussed. The neural network approach is able to uniquely identify the damaged element in almost all of the investigated cases.

Symmetric Structures Made of a Nonlocal Elastic Material

The paper focuses on the analysis of symmetric structures in the context of nonlocal integral elasticity of Eringen-type. In particular, it highlights how the standard (local-type) concept of structural symmetry cannot be applied in a straightforward manner, but it has to be redefined involving an enlarged symmetric model of the structure. Such enlarged model is indeed able to take into account the nonlocal effects exerted on the (standard) symmetric portion of the structure chosen for the analysis by the portion neglected. The appropriate boundary conditions that have to be applied to the enlarged symmetric model for guaranteeing the exact matching between the mirrored symmetric solution and the complete one, are also discussed. Two numerical examples are solved by means of a nonlocal version of the finite element method and the results obtained are critically discussed.

LIMIT STATE EVALUATION OF STEEL-REINFORCED CONCRETE ELEMENTS BY VON MISES AND MENÉTREY–WILLAM-TYPE YIELD CRITERIA

An advanced version of a recently developed numerical limit analysis procedure for the prediction of peak loads and failure modes of steel-reinforced concrete elements is proposed. The modified procedure allows to take into account possible yielding of reinforcement thus capturing the actual behavior at the collapse of both steel and concrete. This implies a finite element (FE) modeling of the reinforced concrete (RC) elements in which concrete is governed by a Menetrey–Willam-type yield criterion, with cap in compression, while steel bars are governed by a von Mises yield criterion. The peak load of a wide range of RC structures whose behavior at ultimate state is dominated either by the concrete crushing or by the steel bars yielding is then predicted with a very good accuracy.

One‐Dimensional Visco‐Elastoplastic Constitutive Model for Asphalt Concrete

This paper proposes a new visco‐elastoplastic constitutive model for asphalt concretes able to reproduce the non linear time‐dependent behaviour of such materials.The constitutive model has been developed with the aim of making it fit specific experimental features previously observed. Moreover the proposed formulation will be demonstrated to be fully consistent with general thermodynamic requirements. Apart from a rigorous analytical formulation; a corresponding rheological sketch of the model is also given. From this representation, it can be shown that the model is essentially a combination of a generalized Maxwell model and a hardening visco‐plastic element.

Mechanical testing and numerical modelling of pull-wound carbon-epoxy spinnaker poles

The paper deals with experimental testing and numerical simulation of the mechanical behaviour of multi-layer cylindrical coupons, of two different diameters, made in carbon-epoxy composite. The aim of the study is to provide a simple and effective numerical model that can be used as a design tool for structural elements having analogous geometrical and manufacturing characteristics. The numerical analysis, performed in the elastic regime with a standard finite element (FE) code, was strongly correlated with the laboratory determination of fibre-volume fractions and of some elastic parameters of the material system. Other parameters, like the shear modulus values G, were in fact appropriately chosen to calibrate the numerical FE model which was forced to reproduce the results of the initial specific ring stiffness tests carried out on pole coupons with external diameter equal to 80 mm. The model was, then, validated by comparison between the numerical results and the experimental ones obtained for coupons of 60 mm diameter.

Limit Analysis of Orthotropic Laminates by Linear Matching Method

A numerical procedure for limit analysis of orthotropic composite laminates, in plane stress conditions, is presented. The procedure can be viewed as an extension, in the context of orthotropic materials, of a method known in the relevant literature as Linear Matching Method. The structural elements here examined are composite laminates obeying, by hypothesis, to a Tsai-Wu type yield criterion. Following the kinematic approach of limit analysis theory, an upper bound to the collapse load multiplier is detected in a finite element context and in an iterative fashion. A few numerical examples are carried out to verify the effectiveness of the proposed approach and to inquire into its capability to predict experimental test results for pinned-joint composite plates.

Structural symmetry within nonlocal integral elasticity: theoretical issues and computational strategies

Abstract The structural symmetry and the appropriate definition of a reduced (symmetric) mechanical/ numerical model is discussed within a nonlocal elasticity context. In particular, reference is made to an integral model of Eringen-type. The paper highlights how the classical, i.e. local, concepts of structural symmetry have to be rephrased through the definition of an enlarged symmetric model of the analyzed structure. This enlarged model, endowed with apposite nonlocal boundary conditions enforced in an iterative fashion, is proved to be able to recover the nonlocal effects that the neglected portion of the structure exerts on the portion chosen for the analysis. It is shown how the mirrored symmetric solution exactly matches the complete one. Theoretical issues and computational strategies referred to a nonlocal version of the finite element method are discussed with reference to the analysis of a case-study.

Limit Analysis on RC-Structures by a Multi-yield-criteria Numerical Approach

The present study proposes a multi-yield-criteria limit analysis numerical procedure for the prediction of peak loads and failure modes of reinforced concrete (RC) elements. The proposed procedure, which is a generalization of a previous one recently presented by the authors, is hereafter applied to structural elements reinforced either with traditional steel bars and stirrups or with fiber reinforced polymer (FRP) sheets used as strengthening system. The procedure allows to take into account the actual behaviour, at a state of incipient collapse, of steel, FRP and concrete by a finite element (FE) based plasticity approach where concrete is governed by a Menetrey-Willam-type yield criterion, FRP reinforcement obey to a Tsai-Wu-type yield criterion and steel reinforcement follow the von Mises yield criterion. To check the effectiveness and reliability of the numerically detected peak loads and failure modes a comparison with experimental laboratory findings, available in literature for large-scale specimens, is presented.